1. Field of the Invention
This invention generally relates to cutting apparatus and method comprising means to convey a workpiece relative to a tool station; and more specifically relates to a pusher preferably built into a rip fence for a table saw.
2. Background Information
Table saws having a portion of a motor-driven circular blade extending upwards through a slot in a saw table are commonly used for rip-sawing narrow strips of wood from a large stock piece. This practice is inherently dangerous and the danger is somewhat reduced by the use of any one of a number of known rip fences. Each of these fences has a straight, flat guide face and can be clamped or locked to the saw table so that the guide face is parallel to the plane of the saw blade. The simplest rip fence may consist of a straight, flat, wooden board clamped to the top of the saw table with individual clamps. The usual, mass-produced, rip fence is fabricated from steel. It can be slid toward or away from the blade on guide rails attached to the front and rear of the saw table. The front of this fence is equipped with a lever for locking both front and rear ends of the fence to the guide rails when depressed.
The manner of rip-sawing wood by hand is the same no matter what kind of rip fence is utilized. The woodworker adjusts the distance between the guide face and the adjacent side of the saw blade to equal the width of the piece he wishes to rip off. He clamps or locks the fence to the saw table in the desired position with the fence parallel to the saw blade and turns the saw on. The woodworker then begins to advance the stock piece of wood into the rotating saw blade by pushing the stock with both hands. As he does this, he must simultaneously hold the stock piece firmly down on the saw table while guiding one straight edge of the stock piece along the rip fence""s guide face. That is, he must press the stock piece down on the table and also push it laterally against the rip fence as he advances the stock piece toward the saw blade. To keep his fingers from being cut by the rotating blade, he must keep them a safe distance from the blade at all times. If the desired width of cut exceeds about two inches, the woodworker may feel confident enough to push the rear end of the wood past the blade with one or more fingers of his or her dominant hand, while reaching beyond the tool with the other hand so as to exert pressure on the cut end to hold it against the table and against the guide face of the rip fence. As the blade cuts through the wood, his finger (or fingers) must enter the narrow space between rip fence and saw blade as he pushes the wood past the blade. When using this technique to rip off very narrow pieces, however, there is always the danger that the blade will cut a finger.
While rip-sawing pieces of any width off a stock piece, an accident called xe2x80x9ckickbackxe2x80x9d can occur if the woodworker accidentally allows the already cut end of the stock piece to angle away from the guide face by even a tiny amount. If the cut end is caught by the far, or outfeed, end of the saw blade, where the blade""s teeth are rising through the table""s slot, the rising and backward-moving teeth snag the wood piece, kicking it off the table and towards the woodworker. The hand grasping the cut end often is pulled back into the saw blade and badly lacerated by the rotating blade. A wood piece may be kicked back with such force that it may itself lacerate a hand or drive splinters into the hand.
To minimize the risk of cutting his hands, the experienced woodworker may use a push stick instead of his fingers to advance the stock piece. As the push stick traverses the narrow corridor between saw blade and fence, however, it may accidentally contact the rotating blade. When this occurs, the push stick can itself be kicked backward into the hand holding it. This sometimes results in a lacerated hand or, at the very least, a bruised one. Push sticks have one major disadvantagexe2x80x94when using one it is difficult to keep the stock piece pressed laterally against the guide face of the fence while it is being pushed forward and past the blade. If the stock piece is allowed to drift off the fence""s guide face at the infeed end, the ripped piece will not have a uniform width along its length; if the stock is allowed to drift off that guide face at the outfeed end, a kickback may occur.
Commercially available hold-down devices, such as those sold under the trade names of Shop Helper ((trademark)), Ripstrate((trademark)), or Leichtung((trademark)), can be clamped to a rip fence to aid in rip-sawing wood. These devices tend to hold the stock piece down and press it laterally against the rip fence. However, a push stick must still be used to advance the wood into the blade toward the end of the cut. The arms of the various hold-down devices traverse the corridor between rip fence and saw blade. The arms, therefore, are obstructions that prevent a push stick from pushing the wood all the way past the saw blade. When rip-sawing with one of these devices clamped on the rip fence, the woodworker pushes the stock piece as far into the blade as he safely can with his hands or a push stick. Then, to complete the cut, he must walk around to the outfeed end of the table saw, grasp the cut end and pull the stock piece through the saw blade.
There are other devices, such as featherboards, which can be used in both horizontal and vertical positions to assist in the ripping operation. A horizontal featherboard can be clamped to the top surface of the table saw to push the stock piece against the guide face of the rip fence. It can only be positioned at the infeed end of the saw (if one is positioned at the outfeed end, it will squeeze the saw kerf and may cause a kickback). Vertically positioned featherboards can be used to hold down the stock piece down on the table. These may be placed at both infeed and outfeed ends. These vertically positioned featherboards usually are clamped to the rip fence, where they obstruct the passage of a push stick. A featherboard will help hold the stock piece down on the saw table. It cannot be set up to press the piece laterally against the rip fence, however. Because featherboards are clamped to the rip fence, they also obstruct the passage of a push stick.
Expensive, motor-powered, rubber-tired feeders may be purchased for rip-sawing wood. A power feeder will simultaneously advance the workpiece while holding it down and pressing it laterally against the rip fence""s guide face. They work well, but can require considerable set-up and adjustment time for accurate rip-sawing. Commercial woodworking shops find power feeders invaluable for safely rip-sawing a large number of pieces of identical width, but most amateur woodworkers cannot afford them. Moreover, a woodworker who does use one may prefer to use a simple push stick when rip-sawing only one or two pieces. To rip-saw off very narrow pieces, the power feeder sometimes must be lowered down so that it straddles the saw blade. During subsequent rip-sawing the blade will cut partly into some of the rubber tires.
Although the use of a table saw is of considerable concern for the invention, and is generally used as an example hereinafter, it may be noted that similar concerns arise with many other power woodworking tools in which a workpiece is held against a guide member as it is conveyed along a feed direction to a tool station. For example, a shaper, which commonly has a tool bit spinning at four to five times faster than a table saw blade, presents many of the same hazards as are encountered in the use of a table saw.
Notable among patent references in this area are the following:
In U.S. Pat. No. 5,662,019 Denman teaches a workpiece pusher that is retractable from a workpiece-engaging position by rotation about an axis parallel to a workpiece feed direction. It is notable that if Denman""s pusher is allowed to rotate while a workpiece is being sawn, the rotation tends to push the workpiece away from the rip fence. Moreover, if Denman""s pusher is in its workpiece engaging position and a sawyer fails to notice the pusher""s orientation before beginning to rip a workpiece, the cut end of the workpiece will push the pusher to its outfeed limit of travel, at which point the sawing operation will have to be stopped to free the outfeed end of the workpiece.
In U.S. Pat. No. 5,018,562 Adams teaches a woodworking fence comprising a dovetail slot running lengthwise along its top surface. A movable stop or push fixture can be slid along the length of the fence with its dovetail protrusion engaged in the dovetail slot of the fence. This push fixture is used to guide wood pieces held at right angles to the woodworking fence. Adams"" fixture cannot be used for full-thickness rip-sawing operations of narrow pieces inasmuch as the saw blade would cut through or into the bottom of his pusher.
In U.S. Pat. No. 4,485,711 Schnell discloses a straddle block having a vertically adjustable leg adapted to slide along the top surface of a table saw""s rip fence. In rip-sawing a piece of wood stock the straddle block is pushed forward by hand along the rip fence; a stepped-down portion of the leg engages the trailing end of the wood stock piece and the wood advances along with the straddle block. Although the bottom edge of the adjustable leg holds the workpiece down to the saw table; the block cannot press the wood laterally against the guide face of the rip fence to ensure that the ripped piece will be of uniform width. Moreover, devices, such as the Shop Helper((trademark)) or Ripstrate((trademark)), cannot be used with Schnell""s straddle block because they impede its passage along the rip fence""s length. Moreover, if Schnell""s pusher is in its workpiece engaging position and a sawyer fails to notice the pusher""s orientation before ripping a workpiece, the cut end of the workpiece will push the pusher to its outfeed-limit of travel, at which point the sawing operation will have to be stopped to free the outfeed end of the workpiece.
In U.S. Pat. No. 4,026,173 Livick teaches the use of a guide rail on the top surface of an adjustable fence. As the guide rail is pushed along the length of the fence, sharp-pointed work engaging and feeding members advance wood pieces into the saw blade on a table saw. To provide adequate force to advance a wood piece, the points of the members must penetrate the workpiece""s top surface. This is a significant disadvantage inasmuch as the top surface of every ripped piece of wood is marred by puncture marks created by the points of the engaging and feeding members. If the rip-sawing slows down abruptly when the blade encounters a knot or dense area of wood, the points may skid along the top surface as the guide rail continues forward at a uniform rate. When this happens, long linear scratches can be produced on the top surface of a ripped piece of wood. Thus Livick""s wood feeding device cannot be used for the rip-sawing of smoothly-planed wood; it will produce disfiguring puncture marks or linear scratches on the top surfaces of ripped pieces.
Thus, it can be seen that current and past rip fence designs have not fulfilled the need for a device that will allow the rip-sawing of narrow pieces of wood safely.
The invention provides a method and apparatus for conveying a workpiece relative to a tool station. A preferred embodiment of the apparatus comprises a movable portion for pushing the workpiece into the tool and a static workpiece-guiding member. In most preferred embodiments, the invention provides the combination of a rip fence and a workpiece pusher for use with a table saw or shaper, wherein the workpiece pusher is adapted to move along a feed direction (e.g., parallel to a saw blade) for a predetermined distance and is further adapted to move away from the feed direction near at least one end of the predetermined distance. In a preferred embodiments the workpiece pusher is adapted to move away from the feed direction at both ends of the predetermined distance.
A preferred apparatus of the invention allows a sawyer to move the workpiece pusher away from a table saw blade at the infeed side thereof, begin a ripping operation in which he or she manually pushes the workpiece into the saw blade until the trailing end of the workpiece is close enough to the saw blade that the workpiece pusher can engage the trailing end and then be used to push the workpiece the rest of the way past the blade. Moreover, apparatus of this sort allows a sawyer or woodworker to operate a table-mounted cutting tool without using a workpiece pusher of the invention that is installed on the table he is using. In this mode of operation, if the workpiece pusher is incidentally engaged by the leading edge of the workpiece, the workpiece pusher does not jam the workpiece into the tool or into the saw fence or other static workpiece-guiding member.
Some embodiments of the invention comprise a workpiece push tab conveyed by a carriage so that the tab moves along a first portion of the surface of a work table in a work-feeding direction and away from the work-feeding direction (i.e., along a line parallel to the surface but skewed with respect to the feed direction) over at least a second, and commonly a third, portion of the surface.
A preferred workpiece pushing apparatus of the invention comprises a workpiece push tab, a tab carriage, and a track. A preferred push tab comprises a piece of relatively soft metal, such as aluminum, which is removably attached adjacent one of its ends to the carriage so as to permit easy replacement. The preferred track is disposed within a rip fence attached to a saw table. This preferred track comprises an infeed end portion, a workpiece pushing portion, and an outfeed end portion; where the infeed and outfeed end portions are skewed with respect to a feed direction (e.g., to the plane of a saw blade) and where the workpiece pushing portion is parallel to the feed direction. A push handle may be fixedly attached to the tab carriage so that it extends away from the tool. In this case, the hand of a sawyer using the handle is further from the saw blade than is the track. In a preferred embodiment, the workpiece pushing apparatus is combined with a rip fence having a longitudinal slot running horizontally along its vertical guide face so that the push tab extends through the slot over a portion of its range of motion. In some embodiments, the rip fence may comprise a cover portion extending over the track, in which case the cover portion may also have a longitudinal slot through which the optional push handle passes.
Some preferred embodiments provide a rip fence having a conventional smooth and unencumbered top, but having a workpiece pusher protruding through the guide face of the rip fence adjacent a lower edge of the face. An advantage of these embodiments is compatibility with existing anti-kickback safety devices that may be attached to the upper portions of a rip fence and that act to hold the workpiece down to the table and against the face of the rip fence.
An advantage of a preferred embodiment of the invention is that it allows a sawyer to operate the saw while paying no heed to the presence of the workpiece pusher of the invention. Although this mode of operation deprives the sawyer of other advantages of the invention, such operation does not pose the jamming hazard that a sawyer would encounter by ignoring a prior art pusher/fence combination while feeding stock into the pusher portion of that prior art combination. Thus, workpiece feeding apparatus may comprise a pushing member movable from an infeed side of a woodworking tool to an outfeed side thereof, the pushing member adapted to extend outwardly from a vertical guide face of a rip fence and into a space between the rip fence and a woodworking tool when the pushing member is most nearly adjacent the tool, the apparatus characterized in that it does not impede the motion of a workpiece placed on the table more distal from the tool than the pushing member and pushed along the vertical guide face from the infeed side of the tool to the outfeed side thereof by means not comprising the workpiece feeding apparatus.
Although it is believed that the foregoing recital of features and advantages may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages of the invention. Moreover, it may be noted that various embodiments of the invention may provide various combinations of the hereinbefore recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments. Although it is believed that the foregoing recital of features and advantages may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages. Moreover, it may be noted that various embodiments of the invention may provide various combinations of the hereinbefore recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments.